Telephone central offices include switching networks for interconnecting subscribers. As the number of subscribers connected to a given central office increases, the switching network capacity must be able to accommodate corresponding increase in traffic. Known techniques for handling traffic increases have been to fully equip any office which is expected to grow, or to provide discrete growth increments of additional switch capacity. Growth in discrete increments usually requires the addition of significantly more equipment at each step than is actually required adding to the cost of the office. Perhaps more importantly, however, growth in discrete steps has typically required some system downtime at the growth intervals in order to complete the necessary rearrangements of the existing switching equipment. The cost penalties in fully equipping a switching network before such network is needed, can be plainly seen. The present invention is an interconnection and growth method which avoids cost penalties of overequipping a switching network and which allows continuous network growth without system downtime.